1. Field of the Invention
The invention concerns a method of recovering powder, in particular for recycling coating powders in powder-coating installations in which objects to be coated are sprayed with powder, preferably by means of an applied electrostatic charge, before they are subject to a heat treatment converting the powder into a homogeneous and strong covering.
The invention also concerns various embodiments of a device implementing this method and incorporating in particular means for processing the aspirated air-powder mixture, these known means being adapted to operate at a pressure different to atmospheric pressure.
2. Description of the Prior Art
A powder-coating installation, in particular of the electrostatic type, generally comprises a sort of cabin through which the objects to be coated are passed in order to be sprayed with powder. Once covered with a relatively uniform but non-adherent layer, the objects are passed into an oven where the powder is converted into a homogeneous and extremely strong covering. Thus powder-coating processes have certain advantages over paint spraying processes, on the one hand because no solvent evaporates in the vicinity of the installation and on the other hand because the powder which is not deposited on the objects may be recovered and recycled. To do this air is sucked out of the cabin and a known type of aerodynamic separator is used to separate the powder from the air and thus to clean the air. A known type separator device is the "cyclone" which comprises an enclosure with a cylindrical and/or fustoconical wall into which air laden with powder is fed tangentially to create a whirlwind type effect as a result of which, because of the centrifugal force generated, the powder is thrown towards the wall of the enclosure and subsequently recovered therefrom; the cleaned air is taken off through an axial conduit. Other types of separator device may be used.
The effective recovery of the powder, which generally collects in a storage tank at the outlet from this type of separator, raises a problem when the separator is adapted to function at a pressure different to, generally slightly lower than, atmospheric pressure. Solutions to this problem previously proposed have not proven entirely satisfactory:
The simplest solution is periodically to shut down the ventilation system in order to empty the contents of the storage tank, which is generally done by hand. This is hardly feasible in a large-scale installation intended for continuous production. Also, considerable labour is involved.
Automated installations often use a recovery tank comprising a compartment that can be isolated after receiving some of the powder. This compartment is then progressively emptied, in order to recycle the powder contained in it, by pressurizing it. This type of installation is costly and also costly to maintain.
Finally, it is possible to suck the powder out of the storage tank directly using a suction device, provided that sufficient suction can be generated.
The invention proposes a solution that is extremely easy to implement, of low cost, and applicable to continuous production installations.